Vacuum pump



H. C. SNOOK vAcmfM PUMP- Filed June 15 1921 9 v MW? Patented ()ct. 16, 1923.

ourrso STATES PATENT OFFICE.

HOMER C. SNOOK, OF SOUTH ORANGE, NEW JERSEY, ASSIGNOR T WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

VACUUM PUMT'.

Application filed June 16, 1921.

To all whom it may concern:

Be it known that I, HOMER C. SN-00K, a citizen of the United States, residin at South Orange, in the county of Essex, tate 6 of New Jersey, have invented certain new and useful Improvements in Vacuum Pumps, of which the following is a full, clear, concise, and exact description.

This invention relates to. an auxiliary pump adapted to cooperate with a roughing pump for exhausting to low pressures. It is particularly, although not exclusively, useful for the production of high vacua necessary in vacuum tubes of the pure electron discharge type.

In the application of W. G. Houskeeper Serial No. 478,975, filed June 20, 1921, there is disclosed an auxiliary pump in which is employed a pumping medium having at room temperatures a vapor pressure leSS than the pressure desired in pure electron discharge devices, whereby is avoided the use of the liquid air trap necessary in mercury vapor pumps.- A metal such as lead,

2 bismuth. tin or the like is vaporized from a molten puddle of the metal, introduced into thepumping chamber in the form of a jet and caused to act mechanically upon gas admitted to the pumping chamber from the vessel to be exhausted to expel the gas from the pumping chamber in the usual manner, after which the vapor is condensed and returned to the puddle to be vaporized again.

The object of this invention is a simple and elfective pump for producing the jet .of pumping vapor and returning the condensed pumping medium to its sources.

An embodiment of the invention comprises a metallic casing containing a puddle of molten metal maintained at a temperature slightly above the melting point of the metal, a portion of which puddle or another puddle fed therefrom is maintained at a 4.5 temperature for which the vapor pressure of the metal is in excess of the pressure obtainable b a roughing pump to cause the emanation t erefrom of a vapor jet useful as the pumping medium. A shield is pro- 0 vided to lead the condensed metal back into the lower temperature portion of said puddle or into the lower temperature puddle. 20

This invention will be better understood by having reference to the following specification and'accompanying drawing wherein Serial N0. 477,916.

Fig. 1 is an elevation showing the relation between the roughing pump,'the auxiliary medium and is provided with a re-entrant' tubular portion 5 near the inner end of which is provided a artition 6 forming the bottom of a cup 7. t the upper end of the cylinder 4 is provided an integral sleeve 8 spaced from the outer wall of the cylinder to form an annular container 9. The upper end of the sleeve 8 is screw threaded internally and a cap 10 is screwed into the sleeve. Arranged coaxially of the cap is the integral tubular member 11 which extends inwardly a short distance and which connects the roughing pump 1 with the auxiliary pump. A second tubular member 12 leads oif from the cap at right angles to the member 11 and is joined to a glass tube 13, leading to the containers 3, according to the method'disclosed in the patent to W. G. Houskeeper 1,294,466. Threaded into the upper end of the cup 7 is an expanding nozzle 14. Surrounding the nozzle 14 but out of contact therewith is a conical shield 15, the lower end of which extends over and 4.- The lower portion of the cup 7 and the annular chamber 9 between the cylinder 4 and the sleeve 8 are connected by means of a tube 16 of such small diameter that the thermal conductivity of the metal therein is very slight.

Arranged .in the upper end of the reentrant portion 5 is a heating unit which, in this instance. comprises a mass 17 of granular carbon held in place by means of a porcelain insulator 18 through which extends the carbon rod 19. The lower end of the carbon rod and'the lower end of the cylinder 4 are electrically connected to opposite poles of a source of electrical energy An oven 21, having a cap 20 which encloses all of the auxiliary pump and a portion of the member 11, is provided with rests upon the upper edge of the cylinder 7 an electrical heating unit 22 connected to the source of electrical energy 20. The heating unit 22 may be extended to the top of the oven, if desired.

In the operation of this device a metal, such as lead, tin, bismuth or the likehaving temperatures near its meltingpoint, a vapor pressure less than the gas pressure within a vacuum tube of the pure electron discharge type, is placed in the cup 7 and in the annular chamber 2 between the'cylinder 4 and the sleeve 8. A seal 23 of the same metal is provided between the cap 10 and the sleeve 8. The metal in the annular puddle and the Walls of the pump are maintained at a temperature slightly above the melting point of the metal by means of the heating unit 22. The metal in the cup 7 is heated by means of heat generated in the mass of granular carbon to a temperature at which its vapor pressure is approximately l mm. of mercury, whereby is caused.

the emanation therefrom of a jet of vapor which passes into the tubular member 11 through the nozzle 14. This vapor acts mechanically upon the gas admitted to the auxiliary pump from the containers 3 and drives it toward the rou hing pump 1. The vapor is condensed on the inner wall of the tubular member 11 in a liquid condition because this member is at a temperature slightly above the melting point of the metal, flows down the tube, drops on to the shield 14 and is returned to the annular or low temperature puddles. As the metal is vaporized from the inner puddle, metal flows thereinto from the annular puddle through tube 16 under hydrostatic pressure. The operation is thus made continuous. Because of the fact that at temperatures near its melting point the pumpingmedium has a vapor pressure less than the gas pressure with a vacuum tube of the "pure electron discharge type there -is no tendency for the vapor to dissipate into the vessel to be exhausted.

The transfer of heat from the inner puddle to the outer puddle through the tube 16 is prevented because of its small thermal conductivity andthe relatively small thermal conductivity of the column of molten metal Within the tube 16. The high vacuum between the cup 7 and the inner wall of the chamber 9 prevents the transfer of heat from the high temperature puddle to the low temperature puddle. The puddle of metal in the chamber 9 is thus kept at the temperatvre for which its vapor pressure is less than that desired in the vessel to be evacuated. The expanding nozzle 14 gives to the vapor jet a substantially parallel flow so that the jet is effective to drive the gas a considerable distance before condensing on .the sides of the tube 11.

The thermal conduction from, the high temperature nozzle 14 by the shield 15 is made very slight by the use of a material of small specific thermal conductivity for constructing the shield 15; by making 15 of thin material; and by having small area of contact with 14.

.What is claimed is 2-- 1. In a vacuum pump, a puddle of molten metal having two portions, one of which is maintained at a temperature substantially sel to be exhausted, a material in said chamber capable of furnishing a supply of vapor, means for heatinga portion of said material and the walls of said chamber, and means for heating the remaining portion of said material to a higher temperaturewhereby the vapor stream used for pumping will emanate from the last mentioned portion of the vaporizable material.

3. In a vacuum pump, a chamber, a supply of material in said chamber capable of furnishing a pumping vapor, means for maintaining said supply of material and the Walls of said chamber at a temperature slightly above the melting point of said material, a second supply of said material in communication with said first supply, and

means for heating saidsecond supply of material to a higher temperature whereb the vapor stream used for pumping wil emanate from said last named supply of material.

4. In a vacuum pump, a chamber, a supply of material in said chamber capable of furnishing a pumping vapor, means for lllll maintaining said supply of material and the walls of said chamber at a temperature slightly above the melting point of said, material, a second supply of said material in communication with said first supply, and means for heating said second supply of material to a higher temperature whereby the vapor stream used for pum ing will emanate from said last named supply of material, and means for causing the metal condensed from the vapor stream toreturn to the low temperature supply.

5. In a vacuum pump, a chamber, asupply.of material in said chamber capable of furnishing a pumping vapor, means for maintaining a portion of said material and the walls of said chamber at a temperature slightly above the melting point of said matherefrom.

6. In a vacuum pump, a chamber, a supply of material in said chamber capable of furnishing a pumping vapor, means [for maintaining a portion of said material and the walls of said chamber at a temperature slightly above the melting point of saidmaterial, a heating unit for maintaining the remaining portion at a temperature suliiciently high to cause the emanation of a vapor stream therefrom, and means for causing the metal condensed from the vapor stream to return to the low temperature portion of the supply.

'Z. In a vacuum pump, a chamber; a supply of material in said chamber capable of furnishing a pumping vapor, means for maintaining a portion of said material and the walls of said chamber at a, temperature slightly above the melting point of said material, and an electrical heating unit in close relation with the remaining portion for heating said material to cause the emanation therefrom of a jet of vapor.

.8. In a pump, a chamber, a supply of material in said chamber capable of furnishing a pumping vapor, means for maintaining a portion of said material and the walls of said chamber at a temperature slightly above the melting point of said material, an electrical resistance heating unit in close relation with the remaining portion for heating said material to cause the emanation therefrom of a jet of vapor.

9. In a pump, a chamber, a supply of material in said chamber capable of furnishing a pumping vapor, a container therefor, means for maintaining a portion of said material and the walls of said chamber at a temperature slightly above the melting point of said material, a mass of granular carbon in contact with a portion of the bottom of the container, and means for supplying current thereto.

10. In a pump, a plurality of containers therein, a tubular connection between said containers, a mass of granular carbon in contact with the bottom of one container, and means for supplying current thereto.

11. In a pump, a plurality of containers, a heat insulating tubular connection between said containers, a mass of granular carbon in contact with the bottom of one of said containers, and means for supplying current thereto.

12. In a pump, a chamber, a supply of material in said chamber capable of furnishing the pumping vapor, electrical means for heating a portion of said material to cause the emanation therefrom of a vapor stream, electrical means for heating the remaining portion of said material and the walls of said chamber, and a common source of electrical energy for both of said heating means.

13. In a pump, a metal cylinder having a re-entrant hollow portion, a container 1ntegral with said re-entrant portion, an annular container concentric with said first container, a cover for said cylinder, said cover having an opening therethrough, a tubular connection between said containers, and a heating element in said re-entrant portion. a

14. In a pump, a metal cylinder having a re-entrant hollow portion, a container integral wit-h said re-entrant portion, an annular container concentric with said first container, a heat insulating tubular connection between said containers, and a heatin element in said re-entrant portion.

15. In a pump, a metal cylinder having a re-entrant hollow portion, a container integral with said re-entrant portion, a mass of granular carbon arranged at the inner end of said re-entrant portlon, and electrical means for passing current through said carbon mass.

16. In a pump, a metal cylinder having a re-entrant hollow portion, a container integral with said re-entrant portion, a mass of granular carbon arranged at the inner end of said re-entrant portion, an insulating block in said re-entrant portion, a carbon rod extending through said block into the granular carbon, and electrical connections between said rod and said cylinder with a source of electrical energy.

17. In a vacuum pump, a metal cylinder having a re-entrant hollow portion, a container integral with said re-entrant portion, an annular container concentric with said first container, a nozzle carried by said inner container, a conical shield extending from said nozzle over the inner wall of said annular container, a tubular connection between said containers and means for heating material in said containers.

18. In a pump, a metal cylinder having a hollow re-entrant portion, a container integral with said re'entrant portion, and a heating element arranged within said reentrant portion.

19. In a pump, a plurality of connected puddles of pumping medium, and means for heating said puddles to diiferent temperatures, said puddles being thermally insulated from each other.

20. In a pump, a plurality of puddles of pumping medium, and means for heating each of said puddles to a difierent temperature.

21. In a pump, a plurality of puddles of pumping medium, and means to heat one of said puddles to the melting temperature of said medium and the other to higher temperature;

pure electron discharge type, causing the em.-

anation from one of said puddles of a vapor jet, utilizing said vapor jet to entrain gas from a vessel being exhausted, condensing said pumping medium to its liquid form, and causingit to flow into the other of said puddles.

23. The method of operating a vapor pump which consists in utilizing as a pumping medium a substance having at temperatures near its melting point a vapor pressure less thanthe gas pressure within a vacuum tube of the pure electron discharge type, maintaining a'puddle' of said substance at melting temperatures, heating another puddle to a higher temperature to cause the emanation therefrom of a vapor jet, utilizing said vapor jet to entrain gas from a vessel being exhausted, condensing said substance to liquid form and causing it to flow into the lower temperature puddle.

24. In an auxiliary pump, a pumping chamber, a plurality of puddles of pumping medium having at temperatures near its melting point a vapor pressure less than the gas pressure within a vacuum tube of the pure electron discharge type, means to heat one of said puddles to cause the emanationtherefrom of a vapor 'et, means to maintain said pumping cham er and said other puddle at the melting temperature of said metal, and means to lead the condensed medium into said low temperature puddle.

25. The method of operating a vacuum' pump which comprises heating a puddle of pumping substance to its meltlng temperature heating another puddle of said substance to a higher temperature tocause the emanation therefrom of a vapor stream,

utilizing said vapor stream to entrain gas from a vessel being exhausted, condensing said substance to liquid form and causing it to flow into said low temperature puddle.

26. The method of operating a vacuum pump which comprises heating two puddles of pumping substance to molten condition, causing the emanation of a vapor jet from one of said puddles, utilizing said vapor jet to entrain gas from a vessel being exhausted, and feeding said puddle from said other puddle.

27. The method of operating a vacuum pump which comprises heating a supply of pump substance to molten condition, heating a small portion of said supply to a higher temperature to cause the emanation therefrom of a vapor stream, and utilizing said vapor stream to entrain gas from a vessel being exhausted.

28. The method of operating a vacuum pump which comprises heating a supply of pumping substance to molten condition,

heating a small portion of said supply to a higher temperature to cause the emanation therefrom of a vapor stream, utilizing said vapor stream to entrain gas from a vessel being exhausted, condensing said substance to its liquid condition and returning it' to the low temperature portion of said supply. 29. In a pump, a pumping passage, a conduit leading from the vessel to evacuated to said pumping passage, a container" enclosing said pumping passage, and means for heating said container.

30. In a pump, 'a pumping passage, a conduit leading from the vessel to be exhausted to said pumping passage, a receptacle for the pumping substance, an oven enclosing said parts, and a heater in the oven.

In witness whereof, I hereunto subscribe my name this 14th day of June A. 1)., 1921.

HOMER C. SN'OOK. 

